There is conventionally known a NAND-type flash memory as a rewritable nonvolatile memory.
In a memory system including a NAND-type flash memory, each of a plurality of blocks needs to erase data already written in the block before data write in the block.
On the other hand, to guarantee the reliability, it is necessary for the NAND-type flash memory to detect, before the occurrence of an error, a block with a high probability of write error occurrence.